Re: [PATCH 2/2] Add DMA support for the sh-sci.c serial driver

[Govindraj <govindraj.ti@gmail.com>]

> +static void sci_request_dma(struct uart_port *port)
> +{
> +       struct sci_port *s = to_sci_port(port);
> +       struct sh_dmae_slave *param;
> +       struct dma_chan *chan;
> +       dma_cap_mask_t mask;
> +       int nent;
> +
> +       dev_dbg(port->dev, "%s: port %d DMA %p\n", __func__,
> +               port->line, s->dma_dev);
> +
> +       if (!s->dma_dev)
> +               return;
> +
> +       dma_cap_zero(mask);
> +       dma_cap_set(DMA_SLAVE, mask);
> +
> +       param = &s->param_tx;
> +
> +       /* Slave ID, e.g., SHDMA_SLAVE_SCIF0_TX */
> +       param->slave_id = s->slave_tx;
> +       param->dma_dev = s->dma_dev;
> +
> +       s->cookie_tx = -EINVAL;
> +       chan = dma_request_channel(mask, filter, param);
> +       dev_dbg(port->dev, "%s: TX: got channel %p\n", __func__, chan);
> +       if (chan) {
> +               s->chan_tx = chan;
> +               sg_init_table(&s->sg_tx, 1);
> +               /* UART circular tx buffer is an aligned page. */
> +               BUG_ON((int)port->state->xmit.buf & ~PAGE_MASK);
> +               sg_set_page(&s->sg_tx, virt_to_page(port->state->xmit.buf),
> +                           UART_XMIT_SIZE, (int)port->state->xmit.buf & ~PAGE_MASK);
> +               nent = dma_map_sg(port->dev, &s->sg_tx, 1, DMA_TO_DEVICE);
> +               if (!nent)
> +                       sci_tx_dma_release(s, false);
> +               else
> +                       dev_dbg(port->dev, "%s: mapped %d@%p to %x\n", __func__,
> +                               sg_dma_len(&s->sg_tx),
> +                               port->state->xmit.buf, sg_dma_address(&s->sg_tx));
> +
> +               s->sg_len_tx = nent;
> +
> +               INIT_WORK(&s->work_tx, work_fn_tx);
> +       }
> +
> +       param = &s->param_rx;
> +
> +       /* Slave ID, e.g., SHDMA_SLAVE_SCIF0_RX */
> +       param->slave_id = s->slave_rx;
> +       param->dma_dev = s->dma_dev;
> +
> +       chan = dma_request_channel(mask, filter, param);
> +       dev_dbg(port->dev, "%s: RX: got channel %p\n", __func__, chan);


If dma channel allocation fails how this scenario will be handled,
There is an possibility of dma_request_channel returning -EBUSY,


> +       if (chan) {
> +               dma_addr_t dma[2];
> +               void *buf[2];
> +               int i;
> +
> +               s->chan_rx = chan;
> +
> +               s->buf_len_rx = 2 * max(16, (int)port->fifosize);
> +               buf[0] = dma_alloc_coherent(port->dev, s->buf_len_rx * 2,
> +                                           &dma[0], GFP_KERNEL);
> +
> +               if (!buf[0]) {
> +                       dev_warn(port->dev,
> +                                "failed to allocate dma buffer, using PIO\n");
> +                       sci_rx_dma_release(s, true);
> +                       return;
> +               }
> +
> +               buf[1] = buf[0] + s->buf_len_rx;
> +               dma[1] = dma[0] + s->buf_len_rx;
> +
> +               for (i = 0; i < 2; i++) {
> +                       struct scatterlist *sg = &s->sg_rx[i];
> +
> +                       sg_init_table(sg, 1);
> +                       sg_set_page(sg, virt_to_page(buf[i]), s->buf_len_rx,
> +                                   (int)buf[i] & ~PAGE_MASK);
> +                       sg->dma_address = dma[i];
> +                       sg->dma_length = sg->length;
> +               }
> +
> +               INIT_WORK(&s->work_rx, work_fn_rx);
> +               setup_timer(&s->rx_timer, rx_timer_fn, (unsigned long)s);
> +
> +               sci_submit_rx(s);
> +       }
> +}


---
Regards,
Govindraj.R
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